200 is good for shallow water but the 50 is best for deeper water trolling. It uses more power and has a wider angle. in a 100 feet of water with the 200, i don't see my rigger balls or make out the thermocline. with the 50 I see all 4 balls and can see the thermocline break. I can also watch the fish streak in and out of the rigger balls. I never see that with the 200.
Gpiatt, I have gone thru 4 transducers in the last 10 years. I spoke to a lowrance rep about this once at a show and he told me that if you use the 50khz more, you will burn out your transducer quicker, he said average life of a transducer running most at 50khz is two years so I would bet that you need a new transducer. it sucks because they aren't cheap!!!